Well, the bank I have all my accounts with would only offer me 9% APR, and no other bank would look at me without me having banked with them for three months or having 3 months of proven earnings (which I didn't have as a flight instructor)
Tesco never actually asked for proof of any earnings, just as long as I could afford the repayments by their responsible lending criteria. I already had a credit card with them with around a £4,500 limit. Some banks just want you to be an existing customer with a proven history.
I think you can check your credit score once here for free
Experian CreditExpert Tips, Advice & Help on Improving Your Finances
then pay a fee to check it regularly afterwards. I've never used it, as I've never been denied a loan (other than sitting chatting at various banks I don't bank with and them saying they won't loan me a penny unless I bank with them for at least three months first)